1. Field of the Invention
The present invention relates in general to predicting the level of noise or brake squeal produced by a brake part during braking, and relates in particular to a method and apparatus for defining and quantifying vibration and noise suppression of a brake part as a single number known as the quality factor or Q-factor.
2. Description of Prior Developments
A longstanding problem associated with the use of vehicle brakes is the generation of annoying noise often referred to as brake squeal. Brake rotors and drums, such as used in virtually all transportation vehicles, are generally considered to be the source of a variety of such noises and associated vibrations.
In order to reduce brake noise, brake rotors and drums have been manufactured using materials and processes which tend to reduce the vibrations produced during braking. Typically, the greater the ability of a brake part to damp vibrations, the less apt the part is to make undesirable braking noise.
Brake component manufacturers, as well as brake system designers, manufacturers and assemblers have attempted to control brake system noise by specifying a minimum amount or minimum level of vibration damping inherent in brake components such as brake rotors and brake drums. Unfortunately, conventional vibration damping measuring techniques used to establish and verify vibration damping properties of brake components have not always provided consistent measurements.
That is, prior vibration measuring techniques attempted to quantify vibration damping performance in terms of a quality factor commonly expressed as a dimensionless number referred to as the Q-factor. The lower the Q-factor, the higher the damping performance of the part and the less likely the part is to squeal during use. In order to quantify the amount of vibration damping in a part, the Q-factor is calculated from the product of a constant term of 27.3 multiplied by the resonant frequency of the part in Hertz and divided by the slope of the vibration decay curve of the part.
Although Q-factors have been specified by original equipment manufacturers (OEMs) such as car and truck manufacturers, significant differences in Q-factors have been measured by suppliers and OEMs when measuring the same components. Variations in Q-factor measurement of up to 25 percent have been experienced, even when measuring the same part several times in the same test fixture.
This lack of repeatability in Q-factor measurement can lead to acceptance issues between manufacturers and suppliers regarding the acceptability of brake components. Accordingly, a need exists for a more reliable method and apparatus for measuring vibration damping in brake system components. A particular need exists for a more reliable and repeatable method and apparatus for measuring and quantifying Q-factor.